Reducing TOC in water using ultraviolet light activated aqueous persulfate is known. It is an established method of decomposing organic compounds in water and is discussed in, for instance, U.S. Pat. No. 4,277,438, to Ejzak, which teaches a batch process of preparing water samples for the measurement of TOC by: (1) persulfate addition, (2) irradiation with an extreme dose of UV (which also heats the sample) to activate the persulfate to oxidize any TOC to carbon dioxide and water. U.S. Pat. No. 5,443,991, by Godec et al, teaches a similar method.
U.S. Pat. No. 5,571,419, to Obata et al, discloses a method of producing Ultra Pure Water (UPW) having a low concentration of organic matter. The purification method requires the following process for the water to be treated: (1) pH adjustment to less than 4.5, (2) addition of an oxidizing agent (such as a persulfate salt), (3) heating of the water to preferably a minimum of 110° C. and more preferably to 120° to 170° C., and (4) cooling the water to the temperature required for use.
The prior art also includes references showing an advanced oxidation process to destroy organic compounds in wastewater, including U.S. Pat. No. 5,762,808, to Peyton, and U.S. Pat. No. 6,096,283 to Cooper et al.
However, despite improvements in this technology, there remains a need for an improved method of producing a reliable, continuous source of low TOC UPW for the semiconductor industry and other industries that require ultrapure water with controlled total organic carbon. The present disclosure describes UV activation of persulfate salt to produce high oxidation potential radicals at ambient temperature, in non-pH adjusted water to purify UPW prior to discharge from the Point of Distribution (POD), prior to the Point of Connection (POC) (typically labeled as the Point of Use or POU), and to purify spent UPW for reuse on a continuous basis.